This invention relates to the non-destructive examination of material for the presence of flaws, and more particularly to the detection of flaws by use of gamma radiation.
Nondestructive inspection or examination of various industrial materials by use of radiation techniques, is already well-known. For example, ultrasonic inspection methods have been utilized for detection and measurement of structural flaws associated with nuclear reactor vessels and components thereof such as the Zircaloy tubes of the nuclear reactor fuel rods. However, certain questions have arisen in regard to the reliability and accuracy of such non-destructive inspection methods. Thus, the need for a more reliable, although non-destructive, inspection system still exists not only for nuclear reactor installations but also for industrial materials in general of critical importance to safety in areas such as power plant and defense installations, and in space exploration related environments. Thus, non-destructive and reliable inspection of vessels, pipes, shafts and turbine blades for cracks, voids, discontinuities and other defects or flaws in both near, far and midsurface ranges remains a problem for which better solutions are being constantly sought.
The use of high energy photon type of radiation applied as a collimated bean to a variety of liquid and solid materials for examination thereof by imaging is already known. For example, the use of x-rays or Gamma rays to analyze coal or coke by measurement of radiation scatter is disclosed in U.S. Pat. No. 4,090,074 to Watt et al. Generally, such prior gamma or x-ray analyzing systems include geometrical arrangements for restricting material penetration by the radiation or scatter thereof, as disclosed for example in U.S. Pat. No. 4,423,522 to Harding, in order to accommodate the radiation detector. Such systems are therefore unable to provide sufficiently accurate information with respect to small sized voids, cracks or flaws in the materials being analyzed.
X-ray examination systems utilizing multi-channeled, peak voltage discrimination techniques to detect, size and locate defects is generally known as disclosed for example, in U.S. Pat. No. 4,121,098 to Jagoutz et al. Such prior non-destructive material analyzing systems are preferable to the use of the aforementioned ultrasonic examination methods wherein surface flaws may totally block transmission of ultrasonic waves. However, the x-ray analyzing method as disclosed in the Jagoutz patent is incapable of being reliably applied to a wide variety of materials and for detecting flaws located at different depths within the material being examined.
The use of gamma ray energy sensitive detectors having superior energy resolution characteristics, are generally known as disclosed for example in U.S. Pat. No. 3,949,210 to Eichinger et al. Such radiation detectors are utilized for gamma ray spectroscopy without any disclosed relationship to techniques for detecting, locating and sizing material flaws.
It is therefore an important object of the present invention to provide a non-destructive material inspection system through which flaws may not only be detected from scatter radiation but to also provide reliable and accurate data from which such flaws may be located and the sizes thereof determined.
An additional object of the present invention in accordance with the foregoing object is to provide a non-destructive material inspection or examination system capable of providing reliable and accurate data with respect to the location and size of material flaws regardless of the depth range within which the flaws are located within the material.
Yet other objects of the present invention in accordance with the foregoing objects is to provide a non-destructive material inspection system providing more reliable and accurate measurement of material flaws in a variety of different environments including, but not limited to, industrial, laboratory, power plant and aircraft sites where safety is of critical concern.